This invention relates to starches and flours that are inhibited and to a process for their preparation. The inhibited starches and flours may be used in place of the chemically crosslinked (i.e., chemically inhibited) starches and flours presently used in foods and in the manufacture of industrial products.
Heat/moisture treatment and annealing of starches and/or flours are taught in the literature and distinguished by the amount of water present. xe2x80x9cAnnealingxe2x80x9d involves slurrying a granular starch with excess water at temperatures below the starch""s or flour""s gelatinization temperature. xe2x80x9cHeat/moisture-treatmentxe2x80x9d involves a semi-dry treatment at temperatures below the starch""s or flour""s gelatinization temperature, with no added moisture and with the only moisture present being that normally present in a starch granule (which is typically 10% or more).
In the following discussion, a history of the various heat/moisture and annealing treatments of starch and/or flour is set out.
GB 263,897 (accepted Dec. 24, 1926) discloses an improvement in the heat treatment process of GB 228,829. The process of the ""829 patent involves dry heating flour or wheat to a point at which substantially all of the gluten is rendered non-retainable in a washing test and then blending the treated flour or wheat with untreated flour or wheat to provide a blend having superior strength. The improvement of the ""897 patent is continuing the dry heating, without, however, gelatinizing the starch, for a considerable time beyond that necessary to render all of the gluten non-retainable. xe2x80x9cDry-heatingxe2x80x9d excludes heating in a steam atmosphere or an atmosphere containing considerable quantities of water vapor which would tend to gelatinize the starch. The wheat or flour may contain the usual amount of moisture, preferably not greater than 15%. The heat treatment may exceed 7 hours at 77-93xc2x0 C. (170-200 xc2x0 F.), e.g., 8 to 14 hours at 82xc2x0 C. (180xc2x0 F.) or 6 hours at 100xc2x0 C. (212xc2x0 F.).
GB 530,226 (accepted Dec. 6, 1940) discloses a method for drying a starch cake containing about 40-50% water with hot air or another gas at 149xc2x0 C. (300xc2x0 F.) or above without gelatinizing the starch. The starch cake is disintegrated by milling it to a finely divided state prior to drying.
GB-595,552 (accepted Dec. 9, 1947) discloses treatment of starch, more particularly a corn starch, which involves drying the starch to a relatively low moisture content of 1-2%, not exceeding 3%, and subsequently dry heating the substantially moisture-free starch at 115-126xc2x0 C. for 1 to 3 hours. The treatment is intended to render the starch free from thermophilic bacteria. The starch should not be heated longer than necessary to effect the desired sterilization.
U.S. Pat. No. 3,490,917 (issued Jan. 20, 1970 to C.A.F. Doe et al.) discloses a process for preparing a non-chlorinated cake flour suitable for use in cakes and sponges having a high sugar to flour ratio. The starch or a flour in which the gluten is substantially or completely detached from the starch granules is heated to a temperature of from 100-140xc2x0 C. and then cooled. The conditions are selected so that dextrinization does not occur, e.g., about 15 minutes at 100-115xc2x0 C. and no hold and rapid cooling at the higher temperatures. The heat treatment should be carried out under conditions which allow the water vapor to escape. The reduction in moisture content due to the heat treatment depends upon the temperature employed. At treatment temperatures of 100-105xc2x0 C., the moisture content is reduced from 10-12% to 8-9%, by weight, while at medium and high temperatures the moisture content is typically reduced to 7% or less. Preferably, during cooling the moisture is allowed to reach moisture equilibrium with the atmosphere. The gelatinization temperature of the heat treated starch or flour is approximately 0.5-1xc2x0 C. higher than that of a comparable chlorinated flour or starch. The heating can be carried out in many ways, including heating in a hot air fluidized bed.
U.S. Pat. No. 3,578,497 (issued May 11, 1971 to E. T. Hjermstad) discloses a process for non-chemically improving the paste and gel properties of potato starch and imparting a swelling temperature as much as xe2x88x927 to xe2x88x921xc2x0 C. (to 20 to 30xc2x0 F.) higher. A concentrated suspension (20-40% dry solids) at a neutral pH (5.5-8.0, preferably 6-7.5) is heated either for a long time at a relatively low temperature or for a short time at successively higher temperatures. The suspension is first heated at a temperature below the incipient swelling temperature of the particular batch of starch being treated (preferably 49xc2x0 C.-120xc2x0 F.). Then the temperature is gradually raised until a temperature well above the original swelling temperature is attained. It is essential that swelling be avoided during the different heating periods so that gelatinization does not occur. After this steeping treatment the starch has a higher degree of granular stability. It resists rapid gelatinization and produces a rising or fairly flat viscosity curve on cooling. The pastes are very short textured, non-gumming, non-slimy, cloudy and non-cohesive. They form firm gels on cooling and aging.
U.S. Pat. No. 3,977,897 (issued Aug. 31, 1976 to Wurzburg et al.) discloses a method for preparing non-chemically inhibited amylose-containing starches. Both cereal and root starches can be inhibited, but the inhibition effects are more observable with root starches. Amylose-free starches, such as waxy corn starch, show no or very slight inhibition. The Brabender viscosity of cooked pastes derived from the treated starch was used to determine the inhibition level. Inhibition was indicated by a delayed peak time in the case of the treated corn starch, by the lack of a peak and a higher final viscosity in the case of the treated achira starch, and by the loss of cohesiveness in the case of the treated tapioca starch. The granular starch is suspended in water in the presence of salts which raise the starch""s gelatinization temperature so that the suspension may be heated to high temperatures without causing the starch granules to swell and rupture yielding a gelatinized product. The preferred salts are sodium, ammonium, magnesium or potassium sulfate; sodium, potassium or ammonium chloride; and sodium, potassium or ammonium phosphate. About 10-60 parts of salt are used per 100 parts by weight of starch. Preferably, about 110 to 220 parts of water are used per 100 parts by weight of starch. The suspension is heated at 50-100xc2x0 C., preferably 60-90xc2x0 C., for about 0.5 to 30 hours. The pH of the suspension is maintained at about 3-9, preferably 4-7. Highly alkaline systems, i.e., pH levels above 9 retard inhibition.
U.S. Pat. No. 4,013,799 (issued Mar. 22, 1977, to Smalligan et al.) discloses heating a tapioca starch above its gelatinization temperature with insufficient moisture (15 to 35% by total weight) to produce gelatinization. The starch is heated to 70-130xc2x0 C. for 1 to 72 hours. The starch is used as a thickener in wet, pre-cooked baby foods having a pH below about 4.5.
U.S. Pat. No. 4,303,451 (issued Dec. 1, 1981 Seidel et al.) discloses a method for preparing a pregelatinized waxy maize starch having improved flavor characteristics reminiscent of a tapioca starch. The starch is heat treated at 120-200xc2x0 C. for 15 to 20 minutes. The pregelatinized starch has gel strength and viscosity characteristics suitable for use in pudding mixes.
U.S. Pat. No. 4,303,452 (issued Dec. 1, 1981 Ohira et al.) discloses smoking a waxy maize starch to improve gel strength and impart a smoky taste. In order to counteract the smoke""s acidity and to obtain a final product with a pH of 4-7, the pH of the starch is raised to pH 9-11 before smoking. The preferred water content of the starch during smoking is 10-20%.
The article xe2x80x9cDifferential Scanning Calorimetry of Heat-Moisture Treated Wheat and Potato Starchesxe2x80x9d by J. W. Donovan et al. in Cereal Chemistry, Vol. 60, No. 5, pp. 381-387 (1983) discloses that the gelatinization temperature of the starches increased as a result of the heat/moisture treatment or annealing. See also the article xe2x80x9cA DSC Study Of The Effect Annealing On Gelatinization Behavior Of Corn Starchxe2x80x9d by B. R. Krueger et al. in Journal of Food Science, Vol. 52, No. 3, pp. 715-718 (1987).
U.S. Pat. No. 4,391,836 (issued Jul. 5, 1983 C.-W. Chiu) discloses instant gelling tapioca and potato starches which are non-granular and which have a reduced viscosity. Unmodified potato and tapioca starches do not normally gel. The starches of the patent are rendered non-granular and cold-water-dispersible by forming an aqueous slurry of the native starch at a pH of about 5-12 and then drum-drying the slurry. The starches are rendered gelling by heat treating the drum-dried starch for about 1.5 to 24 hours at 125-180xc2x0 C. to reduce the viscosity to within defined Brabender viscosity limitations.
U.S. Pat. No. 4,491,483 (issued Jan. 1, 1985 W. E. Dudacek et al.) discloses subjecting a semi-moist blend of a granular starch with at least 0.25 wt. % of a fatty acid surfactant and sufficient water (about 10-40 wt. %) to a heat-moisture treatment at from about 50-120xc2x0 C., followed by drying to about 5-15 wt. %, preferably 10 wt. %, moisture. The heat-moisture treated starch-surfactant product is characterized by a hot water dispersibility of from about 60-100% and a higher pasting temperature than the granular starch from which it is derived. Preferably, the treatment takes place in a closed container so that the moisture can be maintained at a constant level. The preferred conditions are 3 to 16 hours at 60-90xc2x0 C. Degradation and dextrinization reactions are undesirable as they destroy the thickening ability of the starch. The use of conditions, such as, e.g., 35 moisture at 90xc2x0 C. for 16 hours results in reduced paste viscosity. It is believed the presence of the surfactant during the treatment permits formation of a complex within the partially swollen starch matrix with straight chain portions of the starch molecules. The limited moisture environment allows complex formation without gelatinization.
Japanese Patent Publication No. 61-254602, (published Dec. 11, 1987) discloses a wet and dry method for heating waxy corn starch and derivatives thereof to impart emulsification properties. The wet or dry starch is heated at 100-200xc2x0 C., preferably 130-150xc2x0 C., for 0.5 to 6 hours. In the dry method, the water content is 10%, preferably 5%, or less. In the wet method, the water content is 5 to 50%, preferably 20-30%. The pH is 3.5-8, preferably 4-5.
The article xe2x80x9cHydrothermal Modification of Starches: The Difference between Annealing and Heat/Moisture-Treatmentxe2x80x9d, by Rolf Stute, Starch/Stxc3xa4rke Vol. 44, No. 6, pp. 205-214 (1992) reports almost identical modifications in the properties of potato starch with annealing and heat/moisture treatments even through the alteration of the granular structure is different. The Brabender curves of the heat/moisture-treated and annealed potato starches show the same typical changes, including a higher gelatinization temperature and a lower peak viscosity or no peak. The DSC curves also show a shift to higher gelatinization temperatures for both treatments. A combined treatment involving annealing a heat/moisture-treated potato starch leads to a further increase in gelatinization temperature without detectable changes in gelatinization enthalpy and with retention of the viscosity changes caused by the heat treatment. A combined treatment involving annealing a heat/moisture-treated potato starch does not lower the gelatinization temperature, when compared to the base starch, and increases the gelatinization temperature at higher heat/moisture treatment levels.
Starches are chemically modified with difunctional reagents, such as phosphorus oxychloride, sodium trimetaphosphate, adipic anhydride, acetic anhydride and epichlorohydrin, to produce chemically crosslinked starches having excellent tolerance to processing variables such as heat, shear, and pH extremes. Such chemically crosslinked (also referred to as xe2x80x9cinhibitedxe2x80x9d starches) provide a desirable smooth texture and possess viscosity stability throughout the processing operation and normal shelf life.
In contrast, unmodified (i.e., non-crosslinked) starches breakdown in viscosity, loose thickening capacity and textural qualities, and behave unpredictably during storage as a result of the stresses encountered during processing. Heat, shear, and/or an extreme pH, especially an acidic pH, tend to fully disrupt the starch granules and disperse the starch.
When native starch granules are dispersed in water and heated, they become hydrated and swell at about 60xc2x0 C., and reach a peak viscosity through the 65xc2x0-95xc2x0 C. range. This increase in viscosity is a desired property in many food and industrial applications and results from the physical force or friction between the highly swollen granules. Swollen, hydrated starch granules, however, are quite fragile. As the starch slurry is held at temperatures of 92xc2x0-95xc2x0 C., the starch granules begin to fragment and the viscosity breaks down. Shear or conditions of extreme pH also tend to disrupt and fragment the granules, so that the starch polymers dissociate and become solubilized, leading to a rapid breakdown from the initially high viscosity.
It has been known that both the swelling of the starch granules and the breakdown in viscosity can be inhibited by treating the starch with chemical reagents that introduce intermolecular bridges or crosslinks between the starch molecules. The crosslinks reinforce the associative hydrogen bonds holding the granules together, restrict the swelling of the starch granules, and consequently inhibit disruption and fragmentation of the granules. Because of this inhibition, crosslinked starches are also called inhibited starches.
Because chemically crosslinked starches are used in many applications where a stable-viscosity starch paste is needed, it would be an advantage in cost, time, and in the reduction of the use of chemicals, if native or modified starch could be inhibited to perform the same as chemically crosslinked starch without the use of chemicals.
Non-pregelatinized starches and flours are thermally inhibited, without the addition of chemical reagents, in a heat treatment process that results in the starch or flour becoming and remaining inhibited. The starches and flours are referred to as xe2x80x9cinhibitedxe2x80x9d or xe2x80x9cthermally-inhibited (abbreviated xe2x80x9cT-Ixe2x80x9d). When these thermally-inhibited starches and flours are dispersed and/or cooked in water, they exhibit the textural and viscosity properties characteristic of a chemically-crosslinked starch. The starch granules are more resistant to viscosity breakdown. This resistance to breakdown results in what is subjectively considered a non-cohesive or xe2x80x9cshortxe2x80x9d textured paste, meaning that the gelatinized starch or flour tends to be salve-like and heavy in viscosity rather than runny or gummy.
The non-pregelatinized thermally-inhibited granular starches and flours exhibit an unchanged or reduced gelatinization temperature. In contrast, most annealed and heat/moisture treated starches show an increased gelatinization temperature. Chemically-crosslinked starches show an unchanged gelatinization temperature. It is believed the overall granular structure of the thermally-inhibited starches and flours has been altered.
The starches and flours that are substantially completely thermally inhibited will resist gelatinization. The starches and flours that are highly inhibited will gelatinize to a limited extent and show a continuing rise in viscosity but will not attain a peak viscosity. The starches and flours that are moderately inhibited will exhibit a lower peak viscosity and a lower percentage breakdown in viscosity compared to the same starch that is not inhibited. The starches and flours that are lightly inhibited will show a slight increase in peak viscosity and a lower percentage breakdown in viscosity compared to the same starch that is not inhibited.
The starches and flours are inhibited by a process which comprises the steps of dehydrating the starch or flour until it is anhydrous or substantially anhydrous and then heat treating the anhydrous or substantially anhydrous starch or flour at a temperature and for a period of time sufficient to inhibit the starch or flour. As used herein, xe2x80x9csubstantially anhydrousxe2x80x9d means containing less than 1% moisture by weight. The dehydration may be a thermal dehydration or a non-thermal dehydration such as alcohol extraction or freeze drying. An optional, but preferred, step is adjusting the pH of the starch or flour to neutral or greater prior to the dehydration step.
Depending on the extent of the heat treatment, various levels of inhibition can be achieved. For example, lightly inhibited, higher viscosity products with little breakdown, as well as highly inhibited, low viscosity products with no breakdown, can be prepared by the thermal inhibition processes described herein.
All starches and flours are suitable for use herein. The thermally-inhibited starches and flours can be derived from any native source. A xe2x80x9cnativexe2x80x9d starch or flour is one as it is found in nature in unmodified form. Typical sources for the starches and flours are cereals, tubers, roots, legumes and fruits. The native source can be corn, pea, potato, sweet potato, banana, barley, wheat, rice, sago, amaranth, tapioca, sorghum, waxy maize, waxy pea, waxy wheat, waxy tapioca, waxy rice, waxy barley, waxy potato, waxy sorghum, starches having an amylose content of 40% or greater and the like. Preferred starches the are waxy starches, potato, tapioca and corn (including waxy maize, waxy tapioca, waxy rice, waxy potato, waxy sorghum, and waxy barley.
The thermal inhibition process may be carried out prior to or after other starch or flour reactions used to modify starch or flour. The starches may be modified by conversion (i.e., acid-, enzyme-, and/or heat-conversion), oxidation, phosphorylation, etherification (e.g., by reaction with propylene oxide), esterification (e.g., by reaction with acetic anhydride or octenylsuccinic anhydride), and/or chemical crosslinking (e.g., by reaction with phosphorus oxychloride or sodium trimetaphosphate). The flours may be modified by bleaching or enzyme conversion. Procedures for modifying starches are described in the Chapter xe2x80x9cStarch and Its Modificationxe2x80x9d by M. W. Rutenberg, pages 22-26 to 22-47, Handbook of Water Soluble Gums and Resins, R. L. Davidson, Editor (McGraw-Hill, Inc., New York, N.Y. 1980).
Native granular starches have a natural pH of about 5.0-6.5. When such starches are heated to temperatures above about 125xc2x0 C. in the presence of water, acid hydrolysis (i.e., degradation) of the starch occurs. This degradation impedes or prevents inhibition. Therefore, the dehydration conditions need to be chosen so that degradation is avoided. Suitable conditions are dehydrating at low temperatures and the starch""s natural pH or dehydrating at higher temperatures after increasing the pH of the starch to neutral or above. As used herein, xe2x80x9cneutralxe2x80x9d covers the range of pH values around pH 7 and is meant to include from about pH 6.5-7.5. A pH of at least 7 is preferred. More preferably, the pH is 7.5-10.5. The most preferred pH range is above 8 to below 10. At a pH above 12, gelatinization more easily occurs. Therefore, pH adjustments below 12 are more effective. It should be noted that the textural and viscosity benefits of the thermal inhibition process tend to be enhanced as the pH is increased, although higher pHs tend to increase browning of the starch or flour during the heat treating step.
To adjust the pH, the non-pregelatinized granular starch or flour is typically slurried in water or another aqueous medium, in a ratio of 1.5 to 2.0 parts of water to 1.0 part of starch or flour, and the pH is raised by the addition of any suitable base. Buffers, such as sodium phosphate, may be used to maintain the pH if needed. Alternatively, a solution of a base may be sprayed onto the powdered starch or flour until the starch or flour attains the desired pH, or an alkaline gas such as ammonia can be infused into the starch or flour. After the pH adjustment, the slurry is then either dewatered and dried, or dried directly, typically to a 2-15% moisture content. These drying procedures are to be distinguished from the thermal inhibition process steps in which the starch or flour is dehydrated to anhydrous or substantially anhydrous and then heat treated.
Suitable bases for use in the pH adjustment step include, but are not limited to, sodium hydroxide, sodium carbonate, tetrasodium pyrophosphate, ammonium orthophosphate, disodium orthophosphate, trisodium phosphate, calcium carbonate, calcium hydroxide, potassium carbonate, and potassium hydroxide, and any other bases approved for use under the applicable regulatory laws. The preferred base is sodium carbonate. It may be possible to use bases not approved provided they can be washed from the starch or flour so that the final product conforms to good manufacturing practices for the desired end use.
A thermal dehydration is carried out by heating the starch or flour in a heating device for a time and at a temperature sufficient to reduce the moisture content to less than 1%, preferably 0%. Preferably, the temperatures used are 125xc2x0 C. or less, more preferably 100-120xc2x0 C. The dehydrating temperature can be lower than 100xc2x0 C., but a temperature of at least 100xc2x0 C. will be more efficient for removing moisture.
Representative processes for carrying out a non-thermal dehydration include freeze drying or extracting the water from the starch or flour using a solvent, preferably a hydrophilic solvent, more preferably a hydrophilic solvent which forms an azeotropic mixture with water (e.g., ethanol).
For a laboratory scale dehydration with a solvent, the starch or flour (about 4-5% moisture) is placed in a Soxhlet thimble which is then placed in a Soxhlet apparatus. A suitable solvent is placed in the apparatus, heated to its reflux temperature, and refluxed for a time sufficient to dehydrate the starch or flour. Since during the refluxing the solvent is condensed onto the starch or flour, the starch or flour is exposed to a lower temperature than the solvent""s boiling point. For example, during ethanol extraction the temperature of the starch is only about 40-50xc2x0 C. even though ethanol""s boiling point is about 78xc2x0 C. When ethanol is used as the solvent, the refluxing is continued for about 17 hours. The extracted starch or flour is removed from the thimble, spread out on a tray, and the excess solvent is allowed to flash off. The time required for ethanol to flash off is about 20-30 minutes. The dehydrated starch or flour is immediately placed in a suitable heating apparatus for the heat treatment. For a commercial scale dehydration any continuous extraction apparatus is suitable.
For dehydration by freeze drying, the starch or flour (4-5% moisture) is placed on a tray and put into a freeze dryer. A suitable bulk tray freeze dryer is available from FTS Systems of Stone Ridge, N.Y. under the trademark Dura-Tap. The freeze dryer is run through a programmed cycle to remove the moisture. The temperature is held constant at about 20xc2x0 C. and a vacuum is drawn to about 50 milliTorr (mT). The starch or flour is removed from the freeze dryer and immediately placed into a suitable heating apparatus for the heat treatment.
After it is dehydrated, the starch or flour is heat treated for a time and at a temperature sufficient to inhibit the starch or flour. The preferred heating temperatures are greater than about 100xc2x0 C. For practical purposes, the upper limit of the heat treating temperature is about 200xc2x0 C. Typical temperatures are 120-180xc2x0 C., preferably 140-160xc2x0 C., most preferably 160xc2x0 C. The temperature selected will depend upon the amount of inhibition desired and the rate at which it is to be achieved.
The time at the final heating temperature will depend upon the level of inhibition desired. When a conventional oven is used, the time ranges from 1 to 20 hours, typically 2 to 5 hours, usually 3.5 to 4.5 hours. When a fluidized bed is used, the times range from 0 minutes to 20 hours, typically 0.5 to 3.0 hours. Longer times are required at lower temperatures to obtain more inhibited starches.
For most applications, the thermal dehydrating and heat treating steps will be continuous and accomplished by the application of heat to the starch or flour beginning from ambient temperature. The moisture will be driven off during the heating and the starch will become anhydrous or substantially anhydrous. Usually, at these initial levels of inhibition, the peak viscosities are higher than the peak viscosities of starches heated for longer times, although there will be greater breakdown in viscosity from the peak viscosity. With continued heat treating, the peak viscosities are lower, but the viscosity breakdowns are less.
The process may be carried out as part of a continuous process involving the extraction of the starch from a plant material.
As will be seen in the following examples, the source of the starch or flour, the initial pH, the dehydrating conditions, the heating time and temperature, and the equipment used are all interrelated variables that affect the amount of inhibition.
The heating steps may be performed at normal pressures, under vacuum or under pressure, and may be accomplished by conventional means known in the art. The preferred method is by the application of dry heat in dry air or in an inert gaseous environment.
The heat treating step can be carried out in the same apparatus in which the thermal dehydration occurs. Most conveniently the process is continuous with the thermal dehydration and heat treating occurring in the same apparatus, as when a fluidized bed is used.
The dehydrating and heat treating apparatus can be any industrial ovens, conventional ovens, microwave ovens, dextrinizers, dryers, mixers and blenders equipped with heating devices and other types of heaters, provided that the apparatus is fitted with a vent to the atmosphere so that moisture does not accumulate and precipitate onto the starch or flour. The preferred apparatus is a fluidized bed. Preferably, the apparatus is equipped with a means for removing water vapor, such as, a vacuum or a blower to sweep air or the fluidizing gas from the head-space of the fluidized bed. Suitable fluidizing gases are air and nitrogen. For safety reasons, it is preferable to use a gas containing less than 12% oxygen.
Superior inhibited starches having high viscosities with low percentage breakdown in viscosity are obtained in shorter times in the fluidized bed than can be achieved using other conventional heating ovens or dryers.
The starches or flours may be inhibited individually or more than one may be inhibited at the same time. They may be inhibited in the presence of other materials or ingredients that would not interfere with the thermal inhibition process or alter the properties of the starch or flour product.
Unless indicated otherwise, all the starches and flours used were granular and were provided by National Starch and Chemical Company of Bridgewater N.J.
The controls were from the same native source as the test samples, were unmodified or modified in the same manner as the test sample, and were at the same pH, unless otherwise indicated. All starches and flours, both test and control samples, were prepared and tested individually.
The pH of the starch samples was raised by slurrying the starch or flour in water at 30-40% solids and adding a sufficient amount of a 5% sodium carbonate solution until the desired pH was reached. All samples were spray dried or flash dried, as conventional in the art (without gelatinization) to about 2-15% moisture, except for the non-thermally dehydrated starches which were generally oven dried (without gelatinization) to about 2-6% moisture.
Measurements of pH, either on samples before or after the thermal inhibition steps, were made on samples consisting of one part starch or flour to four parts water.
Except where a conventional oven or dextrinizer is specified, the test samples were dehydrated and heat treated in a fluidized bed reactor, model number FDR-100, manufactured by Procedyne Corporation of New Brunswick, N.J. The cross-sectional area of the fluidized bed reactor was 0.05 sq meter. The starting bed height was 0.3 to 0.8 meter, but usually 0.77 meter. The fluidizing gas was air, except where otherwise indicated, and the air was used at a velocity of 5-15 meter/min. The sidewalls of the reactor were heated with hot oil, and the fluidizing gas was heated with an electric heater. The samples were loaded to the reactor and then the fluidizing gas was introduced, or the samples were loaded while the fluidizing gas was being introduced. No difference was noted in the samples depending on the order of loading. Unless otherwise specified, the samples were brought from ambient temperature up to no more than 125xc2x0 C. until the samples became anhydrous and were further heated to the specified heat treating temperature. When the heat treating temperature was 160xc2x0 C., the time to reach that temperature was less than three hours.
The moisture level of the samples at the final heating temperature was 0%, except where otherwise stated. Portions of the samples were removed and tested for inhibition at the temperatures and times indicated in the tables.
Unless specified otherwise, the samples were tested for inhibition using the following Brabender Procedures.
All samples, except for corn, tapioca and waxy rice flour, were slurried in a sufficient amount of distilled water to give a 5% anhydrous solids starch slurry. Corn, tapioca, and waxy rice flour were slurried at 6.3% anhydrous solids. The pH was adjusted to pH 3.0 with a sodium citrate/citric acid buffer. The slurry was introduced into the sample cup of a Brabender VISCO Amylo GRAPH fitted with a 350 cm/gram cartridge. The starch slurry was heated rapidly to 92xc2x0 C. and held for 10 minutes.
The peak viscosity and viscosity ten minutes (10xe2x80x2) after peak viscosity were recorded in Brabender Units (BU). The percentage breakdown (xc2x12%) in viscosity was calculated according to the formula:       %    ⁢          xe2x80x83        ⁢    Breakdown    =                    peak        -                  (                      peak            +                          10              xe2x80x2                                )                    peak        xc3x97    100  
where xe2x80x9cpeakxe2x80x9d is the peak viscosity in Brabender Units, and xe2x80x9c(peak+10xe2x80x2)xe2x80x9d is the viscosity in Brabender Units at ten minutes after peak viscosity.
If no peak viscosity was reached, that is, the data indicate a rising curve or a flat curve, the viscosity at 92xc2x0 C. and the viscosity at 30 minutes after attaining 92xc2x0 C. were recorded.
Using data from Brabender curves, inhibition was determined to be present if, when dispersed at 5-6.3% solids in water at 92xc2x0-95xc2x0 C. and pH 3 during the Brabender heating cycle, the Brabender data showed (i) no or almost no viscosity, indicating the starch was so inhibited it did not gelatinize or strongly resisted gelatinization; (ii) a continuous rising viscosity with no peak viscosity, indicating the starch was highly inhibited and gelatinized to a limited extent; (iii) a lower peak viscosity and a lower percentage breakdown in viscosity from peak viscosity compared to a control, indicating a moderate level of inhibition; or (iv) a slight increase in peak viscosity and a lower percentage breakdown compared to a control, indicating a low level of inhibition.
Characterization of a thermally inhibited starch is made more conclusively by reference to a measurement of its viscosity after it is dispersed in water and gelatinized. The instrument used to measure the viscosity is a Brabender VISCO Amylo GRAPH, (manufactured by C.W. Brabender Instruments, Inc., Hackensack, N.J.). The VISCO Amylo GRAPH records the torque required to balance the viscosity that develops when a starch slurry is subjected to a programmed heating cycle. For non-inhibited starches, the cycle passes through the initiation of viscosity, usually at about 60xc2x0-70xc2x0 C., the development of a peak viscosity in the range of 65xc2x0-95xc2x0 C., and any breakdown in viscosity when the starch is held at the elevated temperature, usually 92xc2x0-95xc2x0 C. The record consists of a curve tracing the viscosity through the heating cycle in arbitrary units of measurement termed Brabender Units (BU).
Inhibited starches will show a Brabender curve different from the curve of the same starch that has not been inhibited (hereinafter the control starch). At low levels of inhibition, an inhibited starch will attain a peak viscosity somewhat higher than the peak viscosity of the control, and there may be no decrease in percentage breakdown in viscosity compared to the control. As the amount of inhibition increases, the peak viscosity and the breakdown in viscosity decrease. At high levels of inhibition, the rate of gelatinization and swelling of the granules decreases, the peak viscosity disappears, and with prolonged cooking the Brabender trace becomes a rising curve indicating a slow continuing increase in viscosity. At very high levels of inhibition, starch granules no longer gelatinize, and the Brabender curve remains flat.
Starches or flours with a low to moderate degree of inhibition will exhibit certain textural characteristics when dispersed in an aqueous medium and heated to gelatinization. In the following examples, the starches or flours were determined to be inhibited if a heated gelatinized slurry of the starch or flour exhibited a non-cohesive, smooth texture.
The crosslinked, thermally-inhibited cationic and amphoteric starches (23.0 g) to be tested were combined with 30 ml of an aqueous solution of citric acid monohydrate (prepared by diluting 210.2 g of citric acid monohydrate to 1000 ml in a volumetric flask) and sufficient water was added to make the total charge weight 460.0 g. The slurry is added to the cooking chamber of the Brabender VISCO amylo GRAPH fitted with a 700 cm/gram cartridge and rapidly heated from room temperature to 95xc2x0 C. The peak viscosity (highest viscosity observed) and the viscosity after 30 minutes at 95xc2x0 C. were recorded. The percentage breakdown in viscosity (xc2x12%) was calculated according to the formula       %    ⁢          xe2x80x83        ⁢    Breakdown    =                    Peak        -                  (                      Viscosity            ⁢                          xe2x80x83                        ⁢            after            ⁢                          xe2x80x83                        ⁢                          30              xe2x80x2                        ⁢                          xe2x80x83                        ⁢            at            ⁢                          xe2x80x83                        ⁢            95            ⁢                          xc2x0C              .                                )                    Peak        xc3x97    100  
Test samples are measured using a Model RVT Brookfield Viscometer and the appropriate spindle (the spindle is selected based on the anticipated viscosity of the material). The test sample, usually a cooked starch paste, is placed in position and the spindle is lowered into the sample to the appropriate height. The viscometer is turned on and the spindle is rotated at a constant speed (e.g., 10 or 20 RPM) for at least 3 revolutions before a reading is taken. Using the appropriate conversion factors, the viscosity (in centipoises) of the sample is recorded.
This test measure the flow properties of the starch or flour. A large sheet of heavy Kraft paper (about 6 ft. square) is secured to a flat, level surface with masking tape. Two rings (3 in. and 4 in. in diameter) are clamped onto a ring stand (6xc3x979 in. base and 24 in. rod) in such a way that the base faces in the opposite direction from the rings. The small ring is placed above the larger ring. To keep the funnels stationary, 1 in. pieces of heavy walled vacuum tubing (xc2xc in. base by {fraction (3/16)} in. wall) are cut lengthwise through one wall and fitted equidistantly at 3 locations on each ring. A chemical funnel having a 100 mm top interior diameter (ID) (Kimax 58) is modified by removing the existing stem and annealing a 8 mm I.D. glass tubing 85 mm in length as the stem. The modified funnel is placed in the large ring and the height is adjusted so that the orifice of the funnel is 1xc2x10.1 cm above the paper. A powder funnel having a 60 mm top I.D. and 13 mm stem I.D. (Kimax 29020-04) is placed in the small ring and the ring is lowered as far as possible, i.e., until the clamps meet. The small funnel should be centered above the large funnel with the orifice of the large funnel stem parallel to the paper. Approximately 50 g of the sample to be tested are slowly added to the powder funnel while gently placing the top of an index finger over the orifice of the large funnel so that any sample which overflows the powder funnel does not flow out of the large funnel. The finger is slowly removed from the orifice while taking care not to move the funnel and allow the sample to flow onto the paper. Flow will cease when the top of the pile reaches the orifice of the funnel stem. With a pencil, the circumference of the sample pile is traced as accurately as possible without disturbing the sample. The sample is removed and the radius of the pile is measured. Each sample is run in triplicate. The test is repeated if the funnel stem becomes clogged before the pile meets the funnel orifice or if the pile is disturbed in any way. The funnels are cleaned after each run.
The average radius of the sample pile is calculated and the angle of repose is determined using the following formula:       Tangent    ⁢          xe2x80x83        ⁢          (              angle        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        repose            )        =            height      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      funnel      ⁢              xe2x80x83            ⁢      orifice              average      ⁢              xe2x80x83            ⁢      radius      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      pile      
For determination of the Horiba wet particle size determination, the thermally-inhibited starches were analyzed, according to the instruction manual-version 1.81C, of the Horiba, Model #LA-900, Laser Scattering Particle Size Distribution Analyzer (Horiba Instrument Inc., Irvine, Calif. 92174). This determination requires that the sample be added under agitation to a cup which contains distilled or de-ionized water until a desired concentration is achieved. The software package then automatically initiates the analysis.
A dry blend of 7 g of starch or flour (anhydrous basis) and 14 g of sugar were added to 91 ml of water in a Waring blender cup at low speed, then transferred to a cook-up beaker, allowed to stand for 10 minutes, and then evaluated for viscosity, color, clarity and texture.
Some of the granular non-pregelatinized starch samples were tested for pasting temperature and/or gelatinization temperature using the following procedures.
This test is used to determine the onset of gelatinization, i.e., the pasting temperature. The onset of gelatinization is indicated by an increase in the viscosity of the starch slurry as the starch granules begin to swell.
A 5 g starch sample (anhydrous basis) is placed in the analysis cup of a Model RVA-4 Analyzer and slurried in water at 20% solids. The total charge is 25 g. The cup is placed into the analyzer, rotated at 160 rpm, and heated from an initial temperature of 50xc2x0 C. up to a final temperature of 800C at a rate of 3xc2x0 C./minute. A plot is generated showing time, temperature, and viscosity in centipoises (cP). The pasting temperature is the temperature at which the viscosity reaches 500 cP. Both pasting temperature and pasting time are recorded.
This test provides a quantitative measurement of the enthalpy (xcex94H) of the energy transformation that occurs during the gelatinization of the starch granule. The peak temperature and time required for gelatinization are recorded. A Perkin-Elmer DSC-4 differential scanning calorimeter with data station and large volume high pressure sample cells is used. The cells are prepared by weighing accurately 10 mg of starch (dry basis) and the appropriate amount of distilled water to approximately equal 40 mg of total water weight (moisture of starch and distilled water). The cells are then sealed and allowed to equilibrate overnight at 4xc2x0 C. before being scanned at from 25-150xc2x0 C. at the rate of 10xc2x0 C./minute. An empty cell is used as the blank.
Test samples are measured using a Model RVT Brookfield Viscometer and the appropriate spindle (the spindle is selected based on the anticipated viscosity of the material). The test sample, usually a cooked starch paste, is placed in position and the spindle is lowered into the sample to the appropriate height. The viscometer is turned on and the spindle is rotated at a constant speed (e.g., 10 or 20 rpm) for at least 3 revolutions before a reading is taken. Using the appropriate conversion factors, the viscosity (in centipoises) of the sample is recorded.